Expression of genes encoding neuropeptides, receptors and enzymes in the brain, with emphasis on the hypothalamus, are being studied. We successfully created a knock-out of the vasopressin 1b receptor (V1bR) gene in mice through homologous recombination. These mice are growing normally and we are studying them using a variety of different physiological and behavioral challenges. They are not as aggressive as their wildtype littermates, which presents the opportunity to examine the neurological basis of aggression. They also show mild reduction in social recognition. Various anatomical and physiological parameters are under study currently. We are also studying the vasopressin 1a receptor (V1aR) knockout that, surprising, shows no reduction in aggression. Other aspects of this mouse's phenotype are in early steps of exploration. Double knockouts of the V1aR and V1bR are viable and outward appearances are normal. They will also be studied behaviorally and physiologically. We are attempting to make oxytocin receptor knockouts in which we can conditionally control the expression of that gene. Transgenic mouse lines that express an inducible cre recombinase have been made that will be crossed with the "floxed" oxytocin receptor.